1. Field of the Invention
The present invention relates to a light scanning apparatus.
2. Description of the Related Art
There is an electrophotographic image forming apparatus (not shown) including a light scanning apparatus 250 illustrated in FIGS. 6A and 6B. FIGS. 6A and 6B are perspective views illustrating a configuration of the conventional light scanning apparatus 250 disclosed in Japanese Patent Application Laid-Open No. 2009-271456. FIG. 6A illustrates the light scanning apparatus 250 with a cover 211 closed, and FIG. 6B illustrates the light scanning apparatus 250 with a part of the cover 211 cut out.
The light scanning apparatus 250 includes a housing 213 which includes an optical casing 210 and the cover 211 that hermetically seals the optical casing 210. As illustrated in FIG. 6B, the optical casing 210 contains a semiconductor laser device 201, a collimator lens 201a, a cylindrical lens 202, a rotary polygon mirror 203, a scanner motor 203b, imaging lenses 204a and 204b, and a mirror 205.
The semiconductor laser device 201 emits laser light in accordance with image information input from the outside. The collimator lens 201a collimates the laser light emitted from the semiconductor laser device 201 and outputs a collimated laser light. The cylindrical lens 202 condenses the collimated laser light collimated by the collimator lens 201a on a reflection surface of the rotary polygon mirror 203 in a line shape. The scanner motor 203b rotates the rotary polygon mirror 203. The laser light condensed on the reflection surface of the rotary polygon mirror 203 in a line shape is reflected and deflected by the reflection surface. The reflected and deflected laser light passes through the imaging lenses 204a and 204b, and is reflected at the mirror 205, thus irradiating a photosensitive drum 206 with the laser light via an opening portion 214 of the cover 211 and a dust-proof glass plate 212.
The imaging lenses 204a and 204b functions to image the laser light reflected and deflected by the rotary polygon mirror 203 on the photosensitive drum 206. With rotation of the rotary polygon mirror 203 by the scanner motor 203b, main scanning is performed on the photosensitive drum 206 by the laser light. Further, with rotation driving of the photosensitive drum 206 about an axis of the photosensitive drum 206, sub scanning is performed by the laser light. That is, the imaging lenses 204a and 204b are designed to condense the laser light reflected and deflected by the rotary polygon mirror 203 on the photosensitive drum 206 to form a spot, and to maintain a constant scanning speed of the spot. In this manner, the rotary polygon mirror 203 scans the laser light emitted from the semiconductor laser device 201 on the photosensitive drum 206.
The surface of the photosensitive drum 206 is uniformly charged by a charging device (not shown). The laser light emitted from the semiconductor laser device 201 forms an electrostatic latent image on the photosensitive drum 206 by scanning and exposing the surface of the photosensitive drum 206 that is uniformly charged. Toner is adhered to the electrostatic latent image formed in this manner by a developing device (not shown) so that the electrostatic latent image is developed into a toner image. The toner image developed in this manner is transferred onto a recording medium (not shown) so that an image is formed on the recording medium.
A light intensity of the laser light which scans and exposes the photosensitive drum 206 is related to a density of the toner image. When the light intensity of the laser light is changed temporally or spatially unlike what is intended, the image density on the recording medium may become partially weak or strong, causing a so-called “uneven density”. In particular, when an optical element in the light scanning apparatus 250 is dirty due to dust adhered thereto, the light intensity of the laser light irradiating the photosensitive drum 206 is partially decreased by the dust blocking the laser light, and as a result, the uneven density occurs.
As illustrated in FIGS. 6A and 6B, the light scanning apparatus 250 includes ribs 223a and 223b which are longer than the opening portion 214 along the longitudinal direction of the opening portion 214. Further, the dust-proof glass plate 212 is adhered to the cover 211 to close the opening portion 214 by applying an adhesive longer than the opening portion 214 in a continuous manner between the rib 223a and the dust-proof glass plate 212 and between the rib 223b and the dust-proof glass plate 212. With this configuration, entry of the dust into the light scanning apparatus 250 through the opening portion 214 is prevented.
As described above, in the conventional light scanning apparatus, the dust-proof glass plate (transparent member) and a housing are bonded to each other with an adhesive. Therefore, if the adhesive is erroneously applied on a portion of the transparent member through which the laser light is transmitted, the adhesive may block the laser light scanning the photosensitive drum (image bearing member), possibly causing an uneven image. In order to avoid this situation, the adhesive needs to be applied in an elaborate manner, and thus the adhesive applying work is time-consuming.